This invention relates to a flotation apparatus for removing printing ink, or the like impuritie, from a fiber suspension that was produced from waste paper. The flotation apparatus is positioned within a container which has a feed opening for the suspension that is to be floated in the lower portion of the container, a pump impeller arranged on a drive shaft, and an air-feed conduit.
Printing ink, and the like impurities, are removed from a waste-paper fiber suspension by mixing fine bubbles of air into the suspension. The detached particles of ink and dirt adhere to the surfaces of the bubbles. These air bubbles rise together with the particles of ink and fine particles of dirt adhering to them and can be removed from the suspension as foam on the surface. By the addition of flotation chemicals, such as sodium soap which is converted by the hardness of the water into potassium soap, the flotation effect is increased.
A pump impeller is generally employed for feeding the suspension which is to be floated. Since the air bubbles in the suspension should be in as finely divided a state as possible, the pump impeller has been used at the same time to disperse the air that is introduced via an air-feed conduit. At the same time, intimate mixing of the suspension with the air is obtained. Particularly in large apparatus, this has the disadvantage that the simultaneous transport of air and dispersal of the air bubbles disturbs the drawing-in of the suspension. Due to the admixture of air, the conveying action of the pump impeller is impaired. Accordingly, a compromise between the conveyor performance and the dispersing of the air which is blown in is required.